Tox: pypy3 must use test3.txt, not test.txt

tox.ini

@@ -54,7 +54,7 @@ commands = {toxinidir}/extra/release/removepyc.sh {toxinidir}
 [testenv:pypy3]
 basepython = pypy3
 deps = -r{toxinidir}/requirements/default.txt
-       -r{toxinidir}/requirements/test.txt
+       -r{toxinidir}/requirements/test3.txt
        -r{toxinidir}/requirements/test-ci.txt
        -r{toxinidir}/requirements/dev.txt
 setenv = C_DEBUG_TEST = 1